Field of the Invention
The invention relates to a method for preparing a Neodymium-Iron-Boron Nd—Fe—B based sintered magnet.
Description of the Related Art
Coercivity is a significant index for evaluating the magnetic properties of a Nd—Fe—B based sintered magnet, and a typical method for improving the coercivity of the magnet is to add a heavy rare earth element such as Tb and Dy during the melting process. However, the heavy rare earth element is expensive. In addition, the heavy rare earth element and iron tends to interact to produce an antiferromagnetic coupling effect, thereby reducing the saturation magnetization and the residual magnetization of the Nd—Fe—B based sintered magnet.
To improve the comprehensive magnetic performance and the coercivity of the Nd—Fe—B based sintered magnet, a dual-alloy technology is employed to control Dy to be distributed mainly in the vicinity of the grain boundary. However, the method requires pure heavy rare earth elements for the preparation of heavy rare earth hydrides, which results in high production cost. On the other hand, the heavy rare earth hydrides must be milled into superfines, which involves a complex and difficult production process, and the resulting product has poor homogeneity.